JP3650314B2 - Noise reduction device for converter - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a noise reduction device for a converter that can significantly reduce a noise current, which is a ground leakage current that flows to the ground side of an input power supply during a conversion operation in a converter such as an inverter or a converter.
[0002]
[Prior art]
In recent years, harmonics generated by switching elements such as inverters and converters have increased, and the EMI (electromagnetic interference) problem has been highlighted. In general, when power is supplied to a load by an inverter device, a leakage current as a noise current flows through a stray capacitance C between the load circuit and the frame ground and between the cable wiring to the load and the ground by high-speed switching.
[0003]
FIG. 6 shows a mechanism through which leakage current flows in the inverter device. In the figure, 1 is an AC power source, 2 is a full-wave rectifier circuit for converting AC to DC (there is a PWM converter, but will be described here as a full-wave rectifier circuit), and 3 is an output of the full-wave rectifier circuit 2 DC capacitor connected between terminals P and N, 4 a DC power source such as a battery connected in parallel to DC capacitor 3, 5 an inverter circuit for converting DC to AC, and 6 a load driven by inverter circuit 5 It is. When each of the switching elements Q _{1 to} Q _{6 of the} inverter circuit 5 is turned on / off, a pulse voltage is applied between the terminal of the load 6 and the frame ground. The leakage current I1 flows through the stray capacitance C due to the voltage change rate (dv / dt) at this time. This leakage current I1 flows through a circuit including the DC power supply 4 such as a battery, the load 6 and the ground via the inverter circuit 5, and causes a malfunction of the leakage breaker, an electric shock accident, and the like. Furthermore, there are also new problems such as dielectric breakdown of the load circuit considered to be caused by dv / dt, di / dt when the switching elements Q _{1 to} Q ₆ are turned on / off, or electromagnetic induction disturbance to other electronic devices. Has occurred.
[0004]
A noise reduction circuit of a conventional inverter device will be described with reference to FIG. The configurations of the AC power source 1 to the inverter circuit 5 and the load 6 are the same as those in FIG. The inverter circuit 5 is a general three-phase bridge inverter composed of switching elements Q _{1 to} Q ₆ . The switching elements Q _{1 to} Q ₆ are on / off controlled by PWM pulses from a control circuit (not shown). The output from the inverter circuit 5 is input to each phase circuit terminal of the load 6. Since the load 6 has a stray capacitance C between itself and the ground, when a pulse voltage output from the inverter circuit 5 is applied to the load 6, a leakage current I1 that is a noise current flows to the ground. In such an inverter device, a line filter 7 called an EMI filter is provided as a noise reduction circuit. Although the line filter 7 has a noise removal function, it is difficult to obtain a sufficient noise removal effect as the on / off frequencies of the switching elements Q _{1 to} Q ₆ increase.
[0005]
[Problems to be solved by the invention]
Conventionally, a line filter called an EMI filter has been used as a noise reduction circuit in a converter such as an inverter. However, it has been difficult for the line filter to obtain a sufficient noise removal effect as the on / off frequency of the switching element in the converter increases. On the other hand, by adding a noise reduction circuit consisting of a reactor or a combination of a reactor and a capacitor, it is possible to remove noise in a high frequency range to some extent, but a large reactor is used to enhance the noise removal effect. There is a problem that the noise reduction circuit becomes large and expensive.
[0006]
The present invention has been made in view of the above, and can provide a noise reduction device for a converter that can remove a wide-band noise current from a low frequency range to a high frequency range and can be reduced in size and cost. The purpose is to provide.
[0007]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, the present invention according to claim 1 is a noise reduction device in a converter including an inverter, comprising: a noise detection means for detecting a noise current; and an AC input input via an insulation transformer. Rectification circuit for rectification, two capacitors connected in series between the positive and negative output terminals of this rectification circuit, and the midpoint of the connection being connected to the ground side input power supply line of the converter and the output voltage of the rectification circuit operate A noise reduction circuit including a current control element that is applied as a voltage and through which a noise compensation current flows, and a signal generated by combining a signal generated from a drive signal of a switching element that constitutes the converter and a detection signal of the noise detection means the driving current control element, reducing of the noise current feedforward by a signal component generated from the driving signal of the switching element by And gist that Rutotomoni suppress the noise current by the feedback control by the detection signal component from said noise detection means. With this configuration, when power is supplied to the load by a converter such as an inverter, a leakage current that is a noise current is generated through a stray capacitance between the load circuit and the frame ground by high-speed switching. This noise current flows through the noise reduction circuit to the converter ground side input power line. At this time, the current control element of the noise reduction circuit is driven by a signal obtained by synthesizing the signal generated from the drive signal of the switching element in the converter and the detection signal of the noise detection means, thereby generating a signal component generated from the drive signal of the switching element. Thus, a noise compensation current that reduces the noise current at high speed in a feed-forward manner and suppresses the noise current by feedback control for the detection signal from the noise detection means is generated, and the noise current is canceled by this noise compensation current. By adding a feed-forward control element, it is possible to suppress a high-frequency noise current that is difficult to remove due to a delay element of the feedback control system. In addition, the noise reduction circuit must ensure a constant operating voltage difference with respect to the ground input power line by connecting the midpoint of the two capacitors to the converter ground input power line. Therefore, the noise compensation current for canceling the noise current can be arbitrarily controlled, and the control is not disabled. Furthermore, this operating voltage can be set to a free voltage value regardless of the voltage and capacity applied to the converter such as an inverter because the noise reduction circuit is connected to the AC input system via an insulation transformer. .
[0008]
According to a second aspect of the present invention, in the noise reduction device for a converter according to the first aspect, the noise detecting means is on the input power source side of the converter from a connection point from a connection middle point of the two capacitors. The gist is that they are arranged in the above. With this configuration, the noise current reduced by the noise reduction circuit is detected by the noise detection means.
[0009]
According to a third aspect of the present invention, in the noise reduction device for a converter according to the first aspect, the signal generated from the drive signal of the switching element is a signal of a drive signal for a plurality of switching elements corresponding to each phase of the converter. The gist is that it is an added value. With this configuration, the noise current can be reliably reduced at high speed in a feed forward manner.
[0010]
According to a fourth aspect of the present invention, in the noise reduction device for a converter according to the first aspect, the signal generated from the driving signal for the switching element is a signal having a pattern triggered by a change in the driving signal for the switching element. It becomes the summary. With this configuration, the current control element of the noise reduction circuit triggers when the drive signal of the switching element is changed, so that the noise current can be reliably reduced at high speed in a feed forward manner.
[0011]
According to a fifth aspect of the present invention, in the noise reduction device for a converter according to the first aspect, the connection midpoint of the two capacitors in the noise reduction circuit is replaced with a connection to the ground-side input power line of the converter. The other two capacitors are connected in series between the input power lines of the converter and are connected to the connection midpoint of the other two capacitors. With this configuration, when the input power line of the converter and the converter and its load system have large stray capacitance, the connection midpoint of the other two capacitors becomes a virtual ground point, and a noise compensation current flows through this virtual ground point. This makes it possible to cancel the noise current.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0013]
FIG. 1 is a diagram showing a first embodiment of the present invention. This embodiment is applied to an inverter noise reduction device. First, the configuration of the converter noise reduction device of the present embodiment will be described. The configurations of the AC power source 1 to the inverter circuit 5 and the load 6 are substantially the same as those in FIG. Noise reducing apparatus is composed of a leakage current detector 8, the noise reduction circuit 9 and the arithmetic circuit 10 for generating an output from the drive signal of the switching element Q ₁ to Q ₆ in the inverter circuit 5 as the noise detecting means. The leakage current detector 8 is a zero-phase CT of an annular core made of, for example, ferrite, and detects a leakage current consisting of a difference in current between input power lines. The noise reduction circuit 9 includes a rectifier circuit 14 for full-wave rectification of alternating current from the alternating current power supply 1 input via the insulation transformer 13, and a positive output terminal P ₁ and a negative output terminal N ₁ of the rectifier circuit 14. The two capacitors C ₂ and C ₃ connected in series with each other and the midpoint of connection between them connected to the ground side input power supply line (the negative output terminal N of the full-wave rectifier circuit 2) and the output voltage of the rectifier circuit 14 Are applied as an operating voltage, and two transistors Tr ₁ and Tr ₂ are provided as current control elements through which a noise compensation current flows. The two transistors Tr ₁ and Tr ₂ have opposite polarities, the transistor Tr ₁ is an NPN type, and the transistor Tr ₂ is a PNP type. In both bases (control terminals) of the transistors Tr ₁ and Tr ₂ , a signal generated by the arithmetic circuit 10 based on the drive signals of the switching elements Q _{1 to} Q ₆ of the inverter circuit 5 from the control circuit 11 and a leakage current detector A signal obtained by combining the detected output of 8 with the amplifier 12 which also serves as an adder is given, and the transistors Tr ₁ and Tr ₂ operate in reverse to each other. The emitters of the transistors Tr ₁ and Tr ₂ are connected in common and grounded via a coupling capacitor C ₁ . The transistors Tr ₁ and Tr ₂ in the noise reduction circuit 9 are required to have high frequency and high current amplification. The current returning to the DC power supply 4 through the noise reduction circuit 9 is a current obtained by reducing the leakage current I1, and the leakage current detector 8 detects the current obtained by reducing the leakage current I1. It is necessary to arrange on the 4th side. The arithmetic circuit 10 outputs a (−) signal when each phase output of the inverter circuit 5 becomes the P side, and outputs a (+) signal when it becomes the N side. Here, the drive signals of the switching elements Q _{1 to} Q ₃ that are the upper arms of the inverter circuit 5 are subtracted, and the drive signals of the switching elements Q _{4 to} Q ₆ that are the lower arms are added.
[0014]
Next, the operation of the noise reduction device configured as described above will be described. The AC power source 1 is rectified to a direct current by a full-wave rectifier circuit 2 and connected to a DC capacitor 3 and a DC power source 4. This DC voltage becomes the input voltage of the inverter circuit 5. The switching elements Q _{1 to} Q ₆ of the inverter circuit 5 are on / off controlled by PWM pulses from the control circuit 11, and the load 6 is driven by the output of the inverter circuit 5. As described above, the load 6 has a stray capacitance C between itself and the ground. Therefore, when a pulse voltage that is an output from the inverter circuit 5 is applied to the load 6, a leakage current I 1 that is a noise current flows to the ground via the grounded terminal of the DC power supply 4. At this time, the leakage current detector 8 adds a signal in which the leakage current I1 flowing in the DC circuit is detected in an equivalent manner to the signal matched to the driving signals of the switching elements Q _{1 to} Q ₆ , and the transistor Tr of the noise reduction circuit 9 ₁ and Tr ₂ are driven. Therefore, the drive current obtained by amplifying the output of the leakage current detector 8 with the amplifier 12 flows into the bases of the transistors Tr ₁ and Tr ₂ , and is amplified to inject a current that cancels the leakage current I 1.
[0015]
Here, the operation based on the detection signal from the leakage current detector 8 and the operation of the noise reduction circuit 9 based on the signal generated from the drive signals of the switching elements Q _{1 to} Q ₆ will be described separately.
[0016]
In the former, when the leakage current I1 flows to the earth line of the DC power source 4 from the load 6, to turn on the transistor Tr _2, the input line N of the inverter circuit 5 from the coupling capacitor C ₁ through the transistor Tr ₂ The noise compensation current flows through the connected closed circuit, and the leakage current I1 flowing into the ground terminal of the DC power supply 4 through the ground line is canceled. Further, when the leakage current I1 flows from the DC power supply 4 of the earth line to the load 6, the transistor Tr ₁ is turned on, flowing through the DC input line P of the inverter circuit 5, the transistors Tr _1, the coupling capacitor C ₁ DC The leakage current I1 of the power supply 4 is canceled out.
[0017]
In the latter case, when the switching element Q ₁ of the inverter circuit 5 is turned on, a positive voltage is applied to the load 6, and the leakage current I 1 flows from the load 6 toward the earth line of the DC power supply 4. 10 by turning on the transistor Tr _2, the noise compensation current flows in a closed circuit connected to the input line N of the inverter circuit 5 from the coupling capacitor C ₁ through the transistor Tr _2, the ground terminal of the DC power source 4 through the earth line The leakage current I1 flowing in will be canceled out. Conversely, when the switching element Q ₂ of the inverter circuit 5 is turned on, a negative voltage is applied to the load 6, the leakage current I1 flows toward the load 6 from the DC power supply 4 of the earth line. At this time, operation to turn on the transistor Tr ₁ by the circuit 10, the noise compensation current flows through the closed circuit connected to the input line P of the inverter circuit 5 from the coupling capacitor C ₁ through the transistor Tr _1, the ground terminal of the DC power source 4 through the earth line Will cancel the leakage current I1 flowing into the.
[0018]
As described above, the leakage current is suppressed by the feedback control based on the leakage current detection from the leakage current detector 8, and the transistor Tr ₁ of the noise reduction circuit 9 is determined by a signal that matches the switching signal of the inverter circuit 5 whose operation response is predicted in advance. , by driving the Tr _2, it is possible to reduce the feed-forward manner leakage current. By adding a feed-forward element, it is possible to suppress a high-frequency leakage current that is difficult to remove due to a delay element of the feedback control system.
[0019]
In the present embodiment, the positive side P ₁ of the rectifier circuit 14 can always supply a constant positive voltage with respect to the ground potential. The negative side N ₁ of the rectifier circuit 14 can always supply a constant negative voltage with respect to the ground potential. Therefore, a constant voltage difference can always be ensured with respect to the input power supply line, so that arbitrary control is possible. Further, since the insulation transformer 13 is interposed, it is possible to set a free operating voltage regardless of the voltage and capacity applied to the inverter circuit 5. Therefore, a commercially available current control element can be used, and it is possible to provide a noise reduction device for a converter that has a simple configuration, is small, inexpensive, and can be controlled at high speed.
[0020]
FIG. 2 shows a second embodiment of the present invention. 2 and the third embodiment to be described later, the same or equivalent components in FIG. 1 are denoted by the same reference numerals as those in FIG. . In the present embodiment, the signal generated from the drive signals of the switching elements Q _{1 to} Q ₃ in the arithmetic circuit 10 is changed to a signal pattern triggered by the change of the drive signals in the switching elements Q _{1 to} Q ₃ of the inverter circuit 5. To do. Outputs a negative pulse signal of the switching element Q ₁ to Q ₃ in the upper arm of the inverter circuit 5 from the off when shifts into the ON state, changed to turn on the switching element Q ₄ to Q ₆ of the lower arm from off conversely In some cases, the arithmetic circuit 10 outputs a positive pulse signal. As a result, the same effect as the first embodiment can be expected. The leakage current is suppressed by feedback control based on the detection output of the leakage current detector 8, and the noise reduction circuit 9 is driven by a signal that matches the switching signal of the inverter circuit 5, thereby suppressing high-frequency leakage current in a feed-forward manner. It becomes possible to do.
[0021]
FIG. 3 shows a third embodiment of the present invention. The DC power source 4 is grounded at the neutral point or not grounded. However, the DC power source 4 is connected to the inverter circuit 5 when the installation site is too far away from the cable or the stray capacitance of the device itself. Capacitors 15 and 16 connected in series to the DC power supply line are added. The capacitors 15 and 16 connected in series are installed on the inverter circuit 5 side from the noise reduction circuit 9. The neutral point of the capacitors 15 and 16 is connected to the series connection midpoint of the capacitors C ₂ and C _{3 as} the noise reduction circuit 9.
[0022]
By this connection method, a virtual ground point is created at the neutral point of the capacitors 15 and 16 in which the neutral point which is the ground connection point of the DC power supply 4 is equivalently connected in series, and the capacitor in the noise reduction circuit 9 is formed at the virtual ground point. By connecting the connection midpoints of C ₂ and C ₃ , a noise compensation current for canceling the noise current can be flowed. Even when the DC power supply 4 is insulated and connected by a stray capacitance such as wiring, a noise compensation current can be passed through the virtual ground point at the neutral point of the added capacitors 15 and 16.
[0023]
Even with the DC power supply 4 grounded at the neutral point, the connection midpoint of the capacitors C ₂ and C ₃ in the noise reduction circuit 9 is connected to the neutral point of the capacitors 15 and 16 divided in series from the DC input power supply line. Thus, the leakage current is suppressed by feedback control based on the detection signal from the leakage current detector 8, and the noise reduction circuit 9 is driven by a signal in accordance with the switching signal of the inverter circuit 5, so that the high frequency is fed forward. Leakage current can be suppressed.
[0024]
The positive side P ₁ of the rectifier circuit 14 in the noise reduction circuit 9 can always supply a constant voltage that is positive with respect to the ground potential, and the negative side N ₁ of the rectifier circuit 14 is always constant negative with respect to the ground potential. Can supply voltage. Therefore, the noise reduction circuit 9 that can be set to a free operating voltage regardless of the voltage and capacity applied to the inverter circuit 5 can be used even with the DC power supply 4 that is grounded at the neutral point. Therefore, a commercially available current control element can be used, and it is possible to provide a noise reduction device for a converter that has a simple configuration, is small, inexpensive, and can be controlled at high speed.
[0025]
FIG. 4 shows a fourth embodiment of the present invention. The current that can flow through the transistors Tr ₁ and Tr ₂ is limited by the rated current of the element. Therefore, when the leakage current I1 that is a noise current is large, the leakage current I1 that flows can be controlled by connecting the transistors Tr _n-1 and Tr _n of the noise reduction circuit 9 in parallel as shown in FIG. it can. Note that current control elements capable of such control generally have only a low voltage and a small capacity. Even if a high-voltage and large-capacity transistor is manufactured, the purpose of use is limited, and the cost is extremely low. It will be expensive. Thus, since the noise reduction circuit 9 can set the operating voltage freely through the isolation transformer 13, the current capacity can be increased regardless of the operating voltage by arranging the transistors Tr _n-1 and Tr _n in parallel. It becomes possible to make it.
[0026]
FIG. 5 shows a fifth embodiment of the present invention. A line filter 17 that is an EMI filter is added between the DC power supply 4 and the inverter circuit 5 and on the DC power supply 4 side outside the noise reduction circuit 9.
[0027]
As a result, higher frequency components can be removed together with the operations and effects of the first embodiment. Further, since the leakage current in the low frequency range is attenuated by the noise reduction circuit 9, the EMI filter 17 can be downsized.
[0028]
【The invention's effect】
As described above, according to the first aspect of the present invention, the noise detecting means for detecting the noise current, the rectifier circuit for rectifying the AC input inputted through the insulating transformer, and the positive / negative output terminals of the rectifier circuit Two capacitors connected in series between them and having a midpoint of connection connected to the ground-side input power line of the converter, and a current control element through which the output voltage of the rectifier circuit is applied as an operating voltage and a noise compensation current flows are provided. The current control element is driven by a signal obtained by synthesizing a signal generated from a drive signal of the switching element constituting the converter and a detection signal of the noise detection means, and a drive signal for the switching element. The noise current is reduced in a feed-forward manner by the signal generated from the signal, and the feedback by the detection signal from the noise detecting means. Due to so as to suppress the noise current by the control, the drive-control of the current control element of the noise reduction circuit, the signal component generated from the driving signal of the switching element by adding a feed-forward manner control element, a feedback control system Therefore, it is possible to suppress a high-frequency noise current that is difficult to remove due to a delay element, and to remove a wide-band noise current from a low frequency range to a high frequency range. In addition, since the noise reduction circuit is connected to the AC input system via an isolation transformer, the operating voltage of the current control element is set to a free voltage value regardless of the voltage and capacity applied to the converter such as an inverter. be able to. Therefore, a general commercially available current control element can be used, and the cost and size of the noise reduction circuit can be reduced.
[0029]
According to the second aspect of the present invention, since the noise detecting means is arranged on the input power source side of the converter with respect to the connection point from the connection middle point of the two capacitors, the noise detecting means reduces the noise. The reduced noise current is detected by the circuit, and the noise current can be surely removed by feedback control based on the detected noise current signal.
[0030]
According to the invention of claim 3, since the signal generated from the drive signal of the switching element is the sum of the drive signals for the plurality of switching elements corresponding to the respective phases of the converter, The noise current can be reliably reduced at high speed.
[0031]
According to the invention of claim 4, since the signal generated from the driving signal of the switching element is a signal having a pattern triggered by the change of the driving signal of the switching element, the current control element of the noise reduction circuit is By triggering when the drive signal of the switching element changes, the noise current can be reliably reduced at high speed in a feed forward manner.
[0032]
According to the fifth aspect of the present invention, instead of connecting the connection midpoint of the two capacitors in the noise reduction circuit to the ground-side input power supply line of the converter, the input power supply line of the converter is connected. When the other two capacitors are connected in series and connected to the connection midpoint of the other two capacitors, the other two capacitors are used when the input power line of the converter, the converter and the load system have large stray capacitance. The midpoint of connection of the capacitor is a virtual ground point, and a noise compensation current flows through this virtual ground point, so that the noise current can be canceled. This virtual ground point system is particularly effective when the DC power source that is the input power source of the converter is grounded at a neutral point.
[Brief description of the drawings]
FIG. 1 is a circuit diagram of a noise reduction apparatus for a converter according to a first embodiment of the present invention.
FIG. 2 is a circuit diagram of a second embodiment of the present invention.
FIG. 3 is a circuit diagram of a third embodiment of the present invention.
FIG. 4 is a circuit diagram of a fourth embodiment of the present invention.
FIG. 5 is a circuit diagram of a fifth embodiment of the present invention.
FIG. 6 is a circuit diagram for explaining a mechanism through which leakage current flows in a conventional inverter device.
FIG. 7 is a circuit diagram showing a noise reduction circuit of a conventional inverter device.
[Explanation of symbols]
2 Full-wave rectifier circuit (input power supply)
4 DC power supply (input power supply)
5 Inverter circuit (converter)
6 Load 8 Leakage current detector (noise detection means)
DESCRIPTION OF SYMBOLS 9 Noise reduction circuit 10 Arithmetic circuit 11 Control circuit 12 Amplifier 13 which also serves as an adder 13 Isolation transformer 14 Rectifier circuit 15 and 16 Two other capacitors 17 EMI filters C ₂ and C ₃ Two capacitors Q _{1 to} Q ₆ switching Element Tr ₁ , Tr ₂ transistor (current control element)

Claims (5)

A noise reduction device for a converter including an inverter, comprising a noise detection means for detecting a noise current, a rectifier circuit for rectifying an AC input inputted through an insulation transformer, and a series connection between positive and negative output terminals of the rectifier circuit Noise reduction provided with two capacitors that are connected and whose connection midpoint is connected to the ground side input power supply line of the converter, and a current control element through which the output voltage of the rectifier circuit is applied as an operating voltage and a noise compensation current flows The current control element is driven by a signal obtained by synthesizing a signal generated from a drive signal of the switching element constituting the converter and a detection signal of the noise detection means, and generated from the drive signal of the switching element. The noise current is reduced in a feed-forward manner by the amount of the detected signal and the amount of detection signal from the noise detecting means is reduced. Noise reduction apparatus of a converter which comprises suppressing the noise current by the readback control.   2. The noise reduction device for a converter according to claim 1, wherein the noise detecting means is arranged on an input power source side of the converter with respect to a connection point from a connection middle point of the two capacitors. .   2. The converter noise reduction device according to claim 1, wherein a signal generated from the driving signal of the switching element is an addition value of the driving signals for a plurality of switching elements corresponding to each phase of the converter. 3.   2. The noise reduction device for a converter according to claim 1, wherein the signal generated from the driving signal for the switching element is a signal having a pattern triggered by a change in the driving signal for the switching element.   Instead of connecting the midpoint of the two capacitors in the noise reduction circuit to the ground input power line of the converter, another two capacitors are connected in series between the input power lines of the converter. 2. The noise reduction device for a converter according to claim 1, wherein the noise reduction device is connected to a connection midpoint of the other two capacitors.

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